Generally speaking, alternating current has been detected by the use of di/dt detector coils in connection with various electrical fault detection systems for use with electrical apparatus, and/or with electrical wiring systems in residential, commercial and industrial applications. In such electrical systems, electrical power is generally routed through protection devices to designated branch circuits supplying one or more loads. Suitable overcurrent and/or arcing fault detector devices may be utilized to provide triggering signals for operating circuit protection devices such as circuit breakers, which are designed to interrupt the electrical current upon the detection of certain predefined fault conditions in the circuit. Similar di/dt sensing and fault detector devices may be used for similar purposes in applications other than electrical systems, for example in individual electrically powered devices, such as industrial machinery, commercial equipment, or residential appliances.
Generally speaking, the di/dt sensors for such applications have consisted of toroidal coils having a central through opening, through which the wire or other conductor to be monitored extends.
The construction and use of such toroidal coils is generally well known. However, the toroidal coil heretofore proposed for such arc detection or other current detection applications can be relatively expensive and difficult to mass produce. Examples of such toroidal coils as shown for example in U.S. Pat. applications Ser. No. 08/403,033 filed Mar. 13, 1995 and entitled "Current Sensing Arcing Fault Detector and Method," now abandoned and Ser. No. 08/403,084, filed Mar. 13, 1995 and entitled "Device and Method for Testing Arcing Fault Detectors," now abandoned.
One other device for measuring an electrical current in a conductor utilizes a so-called Rogowski coil, which is generally a printed circuit plate provided with a circular cutout, with a coil being implemented by metal deposits on each of the two faces of the plate and extending along radii such that geometrical projections thereof pass through the center of the cutout. Electrical connections between the radii on the two faces are implemented by plated through holes that pass through the thickness of the plate. Such a Rogowski coil for measuring an electrical current in a conductor is shown for example in U.S. Pat. No. 5,442,280. However, the Rogowski coil as shown in the above-referenced patent is also relatively complicated, expensive and difficult to produce.